1. Field
The present invention relates to a microactuator, an optical device, a display apparatus, an exposure apparatus, and a method for producing a device.
2. Description of the Related Art
In accordance with the development of the MEMS (Micro-Electro-Mechanical System) technique, various microactuators to which the technique is applied, various optical devices such as DMD (Digital Micro-mirror Device) and the like which utilize the technique, various projection display apparatuses which utilize such optical devices, various exposure apparatuses which use such optical devices as variable shaped masks (also referred to as “active masks”), etc. have been suggested.
For example, Japanese Patent No. 3492400 discloses a typical DMD. In this DMD, a mirror is held by a torsion hinge, and the hinge is torsionally deformed by the electrostatic force to rotate the mirror so that the direction of the mirror is changed to change the direction of reflection of the incident light (incident light beam). A plurality of the basic units as described above are aligned one-dimensionally or two-dimensionally to provide a spatial optical modulator which is applied to an optical information processing apparatus, a projection display apparatus, an electrostatic photograph printing apparatus, etc.
An optical device is also known, in which a cantilever beam provided with a mirror is deflected or flexibly bent by the electrostatic force to change the direction of reflection of the incident light (see “Design and Fabrication of the Thin-Film Micromirror Array-actuated for Large Projection Displays (Journal of the Korean Physical Society, Vol. 33, No., November 1998, pp. S467-S470)”).
However, in the microactuator using the torsion hinge, the mirror is held by the torsion hinge. Therefore, the microactuator tends to be damaged or broken by the torsional stress applied to a connecting portion of the torsion hinge, and it has been difficult to prolong the service life thereof. On the other hand, in the microactuator using the cantilever beam, it has been impossible to quicken the response speed, because the natural frequency of the cantilever beam is low.
In view of the above, Japanese Patent Application Laid-open No. 2005-24966 proposes a micromirror device using a bridge beam which has both ends fixed onto a substrate having a V-shaped recess and which is provided to bridge the recess. In this device, a light-reflective film is formed on the bridge beam, and a mirror is integrated with the bridge beam as a whole. In a state in which the electrostatic force is not applied, the bridge beam (i.e., the mirror) has a flat plate-shaped form. On the other hand, when the electrostatic force is applied, the bridge beam (i.e., the mirror) is deformed to have a V-shaped form along with the V-shaped recess in accordance with the electrostatic force to change the direction of reflection of the incident light.
Since this device uses the beam, the damage or breakage hardly occurs and it is possible to realize a long service life as compared with a case in which the torsion hinge is used. Further, it is possible to enhance the natural frequency, and it is possible to quicken the response speed.